This invention relates to a method for controlling an internal combustion engine during engine shutdown to reduce evaporative emissions. In particular, the invention relates to a method for reducing fuel pressure in a fuel rail of the engine, during engine shutdown, to reduce evaporative emissions.
Internal combustion engines are generally controlled to maintain the ratio of air and fuel at or near stoichiometry. In particular, the engines are controlled utilizing closed-loop control where the amount of fuel delivered to the engine is determined primarily by the concentration of oxygen in the exhaust gases. The amount of oxygen in the exhaust gas is indicative of the ratio of air and fuel that has been ignited in the engine.
Known engines sense the oxygen level in the exhaust gases of the engine utilizing a Heated Exhaust Gas Oxygen (HEGO) sensor. Further, known engine control systems adjust the commanded air/fuel ratio of the engine responsive to the output of the HEGO sensor.
Known engines also utilize a three-way catalytic converter to reduce the unwanted by-products of combustion. The ratio of air and fuel may be maintained near stoichiometry for efficient operation of the catalytic converter.
Known engine control systems stop the closed-loop control of an engine when an ignition switch changes to a state that indicates that the engine should be shut down. In particular, the control systems immediately shut off a fuel pump and stop transmitting control signals to fuel injectors of the engine. As a result, the fuel injectors immediately stop supplying fuel to the engine cylinders. Further, known engine fueling systems utilize a check valve to maintain the fuel in a fuel rail at a relatively high pressure after engine shutdown. For purposes of discussion, the term xe2x80x9cfuel railxe2x80x9d means one or more fuel lines supplying fuel to one or more fuel injectors. It has been determined that leaving the fuel in the fuel rail at the relatively high pressure, after engine shutdown, results in increased evaporative emissions.
The present invention provides an automotive vehicle and a method of controlling an internal combustion engine during engine shutdown to reduce evaporative emissions.
An automotive vehicle in accordance with the present invention includes an engine having fuel injectors selectively supplying fuel to cylinders of the engine. The vehicle further includes a fuel pump selectively supplying fuel through a fuel rail to the fuel injectors. The vehicle further includes a controller operatively connected to the fuel injectors and the fuel pump. The controller is configured to shut off the fuel pump upon a change of state of an engine control signal. Finally, the controller is configured to control a duty cycle of the fuel injectors, after said fuel pump is shut off, to allow the engine to operate cyclically about a predetermined air/fuel ratio. Controlling the engine after the fuel pump has been shut off results in the residual fuel in the fuel rail being ignited in the engine cylinders. Thus, the fuel pressure in the fuel rail will be decreased during an engine shutdown time interval resulting in decreased evaporative emissions.
A method of controlling an internal combustion engine during engine shutdown in accordance with the present invention includes a step of shutting off a fuel pump of the engine. The method further includes a step of burning off the fuel from the fuel rail in an engine cylinder after the fuel pump is shut off. During the burning off of the fuel, a duty cycle of a fuel injector is controlled to allow the engine to operate generally cyclically about a predetermined air/fuel ratio. The predetermined air/fuel ratio is preferably stoichiometric.
An automotive vehicle and a method for controlling an internal combustion engine in accordance with the present invention represent a significant improvement over conventional vehicles and methods. In particular, the inventive automotive vehicle and method decreases the fuel pressure in the fuel rail, during an engine shutdown time interval before completely shutting down the engine. As a result, evaporative emissions from the fuel injectors is decreased when the vehicle is not being operated.
These and other features and advantages of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.